1. Field of the Invention
The present invention relates to a vehicle seat including an upper frame (an upper framework of a seatback), plate-shaped side frames (side frameworks of the seatback), and a headrest on an upper part of the seatback.
2. Description of Related Art
As this type of vehicle seat, there has been known a vehicle seat described in Japanese Patent Application Publication No. 2009-136482 (JP 2009-136482 A). The vehicle seat includes a seatback rising from a seat cushion, and a headrest on an upper part of the seatback. A framework (a back frame) of the seatback includes an upper frame and paired side frames. The upper frame is a pipe material (a round steel pipe) having a generally reverse U shape and serving as an upper framework, and its central part is deformed in an upwardly projecting manner, so as to constitute a headrest. Further, each of the side frames is a plate-shaped member serving as a side framework, and an upper side thereof has a curved shape along an outer peripheral surface of the upper frame. In the publicly known technique, both bottom ends of the upper frame are fitted into upper parts of the side frames, and the frames are welded to be integrated with each other.
Here, in the field of the vehicle seat, in consideration that the round steel pipe is relatively expensive, the upper frame may be formed of a flat plate. For example, the upper frame is formed from a flat plate in a hollow box shape (a relatively cheap configuration), and is provided in a holder (a tubular material) in an inserted manner. A headrest stay (in a bar shape) projecting from a lower part of the headrest is provided in the holder in an inserted manner, so that the headrest is attached to an upper part of the seatback. Further, paired side frames are formed from a flat plate, and upper sides thereof are formed in a generally U shape in a traverse sectional view. A front side of each of the side frames is bent toward a seat inward side so as to form a first flange portion, and a rear side of the each of the side frames is bent toward the seat inward side so as to form a second flange portion. Then, the upper frame is placed between the paired side frames in a bridging manner, and each end of the upper frame is placed between the first flange portion and the second flange. Then, the each end of the upper frame is fixed to the flange portions, so that the upper frame can be fixed to the side frame.